1. Field of the Invention
The present invention refers to an apparatus for the clamping of workpieces which have a circular or prismatic, i.e. rectangular, square etc. cross section or which include at least one shaft portion having a circular or prismatic cross section. The apparatus according to the invention is particularly suitable for the clamping of electrode blanks for electro-erosive machining devices, but may be useful in clamping every kind of elongate workpieces or of tools having an elongated shaft portion.
The electrodes used in electroerosive machining devices are tools which have to be clampingly fastened to the device with an extraordinarly high precision, not only with regard to their centricity, but also with regard to their angular position relative to their central axis. Such electrodes are manufactured from blanks, e.g. from prismatic, square or round copper bars, by turning and/or milling and/or grinding, whereby the blank has to be clampingly fastened to the chuck of such turning, milling and grinding device during the machining thereof. In the course of the machining of the blank, a precisely located central axis will be defined in the tool, serving as a reference during the subsequent electroerosive machining process.
The blank having been clampingly fastened to the machining device and having been machined to an electrode body, said theoretical central axis is well defined with reference to the clamping apparatus, and it is most desirable not to have to remove the electrode body from the clamping apparatus anymore. Every subsequent clamping of the tool, even if the clamping apparatus is manufactured to an extremely high standard of precision, results in a more or less pronounced shift of said theoretical central axis with reference to the central axis of the clamping apparatus, such effect being most undesired in view of the extremly high precision standards which have to be met during an electroerosive machining process.
2. Prior Art
Suitable coupling devices for the clamping of electrode bodies to electroerosive machining devices are known, which allow a higly precise centrical clamping including the exact provision of a predetermined angular position of the tools on the electroerosive machining device. In many cases, however, it is not possible to fasten the electrode blank directly to a coupling device of such an apparatus, so that a clamping apparatus to be inserted therebetween will be necessary. Besides the required stability and precision, the clamping apparatus must be as inexpensive as possible, since electrodes for electroerosive machining devices have to be stocked sometimes in lots of several hundreds.
It is admitted that clamping devices for prismatic or circular workpieces are known which may comply with the requirements as far as the precision and stability is concerned, which are however relatively expensive. A storage of several hundreds of electrodes each fastened to such a clamping apparatus, therefore, is a very expensive matter.
A clamping apparatus of the kind described above is known from the disclosure of French Pat. No. 514'448. This apparatus comprises a support member of generally cylindrical configuration, one end thereof being connected to a plain flange member equipped with fastening openings, and the body of the support member is equipped with a longitudinal groove having a V-shaped cross section. Further, there is provided an essentially ring-shaped clamping member equipped with a clamping screw. The clamping member may be pushed onto the cylindrical support member in three different positions, depending of the kind and size of the workpiece to be clamped. This apparatus is comparatively complicated and therefore expensive to manufacture, even if only modest requirements with regard to the precision of the clamping have to be met. Due to the elongate design of this apparatus, being anchored at the flange only by means of the quite small front face, the stability and ruggedness of this apparatus is not sufficient at all, if highest requirements of machining precision have to be fulfilled, e.g. in the case of electroerosive machining.
A storage of the electrodes per se, not being fastened to any clamping apparatus, usually is not possible, as the requirements regarding the precision of an exact positioning may not be met in most cases.